Liquid-cooled engines equipped with cooling means are used, for example, as drive sources in electrical generators, operating machinery, and the like. One known example is the cooling-means equipped engine disclosed, for example, in Japanese Patent Application Laid-Open Publication No. S62-159750 (S62-159750 A), which has an integrally formed cylinder block and cylinder head and a water jacket formed on the cylinder block, and is equipped with cooling means having a cooling passage embedded inside the cylinder head. In this engine, causing a cooling liquid to flow through the water jacket of the cylinder block and through the cooling passage of the cylinder head makes it possible to cool the cylinder block and the cylinder head.
In the past, configuring a water jacket involved dividing the cylinder and the cylinder head to form a conduit. However, this means that the cylinder and the cylinder head are two separate members and that space is needed for fastening bolts, therefore creating problems of difficulty in reducing size and weight, and of an increased number of parts.
Further, in a case where the cylinder and the cylinder head are integrally formed, the conduit is formed in the core, and because a low-pressure die casting fabrication process is employed, problems of lengthy production time and increased production costs are encountered.
A potential countermeasure entails forming a cooling passage to the outside of the cylinder block in place of the water jacket, thereby ensuring ample cooling capacity.
However, in cases where a cooling passage is formed to the outside of the cylinder block, it becomes difficult to maintain compactness of a compact engine. It has accordingly been considered difficult to ensure ample cooling capacity in a state in which compactness of a compact engine is maintained.